World of Warcraft
Kel'Thuzad

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Kel'Thuzad was a powerful human mage, an archmage of the Kirin Tor, and member of the Council of Six until his interest in the dark arts caused him to be stripped of his rank and holdings, and exiled from Dalaran by the Grand Magus Antonidas. Driven by the voice in his head, he traveled to Northrend and climbed the Frozen Throne to offer his soul to the Lich King.
Now a necromancer of the Scourge, Kel'Thuzad returned to Lordaeron and founded in secret the Cult of the Damned, recruiting cultists among the nobility and the lower classes of the kingdoms with promises of immortality. Years later, he became one of the principal agents of the Lich King responsible for spreading the plague of undeath across Lordaeron, resulting in his death at the hands of the paladin and Prince Arthas Menethil. When Arthas became a death knight and started the Scourging of Lordaeron, he resurrected Kel'Thuzad as a lich with the power of the Sunwell, so he could summon Archimonde the Defiler into Azeroth during the Third War.
Following Arthas's departure for Northrend, and his ascension as the new Lich King, Kel'Thuzad was left to command the Scourge in Lordaeron from the floating necropolis of Naxxramas. After making a deal with the nathrezim Balnazzar, he trapped the Highlord of the Silver Hand Alexandros Mograine at Stratholme, and recovered his body to make him the leader of the Four Horsemen and his champion, before replacing him by his son Darion Mograine after the first battle for Light's Hope Chapel. For years he held control of the Plaguelands and fought against the forces of the Scarlet Crusade, the Argent Dawn, the Alliance and the Horde, until his first defeat at the hands of adventurers.